The invention relates to a current limiting switch device comprising a chamber and a conducting deflector housed in an insulating case. The chamber is connected to the outside and houses a fixed piece and a switching piece movable in a plane. These pieces are equipped with contact studs and a control member acting on the mobile piece is moved for making and breaking an electric circuit. The conducting deflector is connected electrically to the fixed piece and extends into the chamber so that one of the feet of the arc appearing on opening may move in the chamber.
Devices corresponding to the above construction are used particularly in apparatus such as circuit-breakers used for protecting industrial or domestic installation lines.
They may, if required, be used in more complex apparatus where remote controlled current making and breaking means are combined, such as contactors.
Protective apparatus of the circuit breaker type require breaking of the current as rapidly as possible when it undergoes an increase corresponding to that which full short-circuit currents would take. Such apparatus should provide not only very considerable limitation of the intensity of the short-circuit currents but also to make the time interval as short as possible during which these currents will flow in the circuit to be protected.
Since the rate of growth of fault currents is controlled by the voltage developed in the arc which appears between the contacts at the time of opening, this voltage must reach levels as high as possible, considering the supply voltage of the mains.
Prior art methods for increasing the voltage of the arc include adjusting its length, its temperature and its section. For increasing the arc length one communicates to the contacts as wide a spacing as possible in an extremely short time, which requires the use of a comparatively large energy.
It is also known to provide the cut-off chambers in which the switches are disposed, with a multiplicity of metal fins or good heat-conducting fins, so that an arc which is formed thereon is subjected to considerable cooling. An embodiment of this technique, which is still widely used, requires the manufacture, assembly and mounting of fins whose technical cost is relatively high, all the more so since the apparatus is of small size. Moreover, the volume required for positioning such fins requires that there is relative freedom in the choice of dimensions, a situation which occurs less and less frequently, particularly when dimensional standards govern the size of such apparatus.
For increasing the arc voltage, one has priorly used the interaction of a magnetic field with the current so as to promote the natural development of the arc or an insulating screen for extending its arc and/or greatly reducing the section of the arc by choking it against an insulating wall.